Vacuum metallizing of plastic and similar dielectric substrates is disclosed in various forms including U.S. Pat. Nos.
2,992,125; Fustier PA2 2,993,806; Fisher PA2 3,118,781; Downing PA2 3,914,472; Nakanishi PA2 4,101,698; Dunning PA2 4,131,530; Blum PA2 4,211,822; Kaufman PA2 4,215,170; Oliva
My prior U.S. Pat. No. 4,431,711 issued Feb. 14, 1984, relates to metal film island structure and spacing to the appearance and performance of a commercial product, to the conductivity of the metal layer, to the corrosion resistance of the metal layer and/or to the adhesion of the top coat. It further relates to nucleation and film growth to a desired island structure and spacing that achieves these ends.
With regard to the last statement, two excellent reference books are:
Thin Film Phenomena, Kasturi L. Chopra, Robert E. Kreiger Publishing Company, Huntington, N.Y., 1979. See especially pp. 163 et seq. PA1 Handbook of Thin Film Technology, Leon I. Maissel and Reinhard Glang, McGraw-Hill Book Company, New York, N.Y., 1970. See especially pp. 8-32 et seq.
These texts discuss and illustrate the stages of metal film growth by vacuum deposition from metal nucleation and nuclei growth, to liquid coalescence, to electrically discrete islands, channelization with incipient film conductivity, and finally, full continuous film formation. Film formation of vacuum deposited metals on plastic substrates for commercial products, especially on elastomeric plastic substrates, is not discussed. Nor is the interdependence of the natures of the metal film and the top coating correlated with product performance.
My U.S. Pat. No. 4,431,711 shows the significant difference in performance to be obtained with a vacuum metallized flexible plastic product, top coated, where the metal particles are coalesced only to the island state instead of being allowed to coalesce to beyond the channelization stage where film conductivity is established.
In the '711 patent, the separate islands are coalesced from separate nucleation points and are globular or rounded and fused appearing and are part of the nucleation and growth process.
In general, the coalesced islands forming the indium films of the '711 patent are smaller and there is a much greater spacing between them that can be filled with the resin of the top coating, in effect encapsulating the islands and binding them to the substrate surface. The rounded islands are better protected by the resin and the film over all is far more corrosion resistant, surprisingly so. The metal film is much more securely adhered to the substrate--a very significant advantage. The appearance of the globular island product is better--it is more specular, more reflective.
The construction of the indium island structure in U.S. Pat. No. 4,431,711 includes islands that are separated by channels which receive the top coat to bond the resinous film of the top coat to the substrate for the indium island structures. While the island structures are suitable for their intended purpose, it has been observed that the channels formed between the individual islands also contain many clusters and smaller islands of residual material. It is believed that this material reduces the total effective area of substrate material to which the top coat can be bonded. Consequently, the resultant bright trim article may be subject to undesirable delamination between the top coat and the substrate material.
The prior art does not set forth a proven process for forming a clear channel configuration by use of etchants so as to improve adhesion of a top coat.